Chicago (CBS) -- The organizers for Sunday's interfaith service expect around 700 people to attend, but that number could grow to over a thousand.
Among the people attending the vigil is a woman who grew up in Pittsburgh and knows two victims of the shooting.
"That was our congregation," Mari Holzer said. "My husband's cousin was a 97-year-old Holocaust survivor whose life was taken in that bloodbath and whose daughter, who takes her every Saturday morning religiously, was wounded."
Oren Jacboson, one of the service's organizers, spoke about how the massacre has brought fear to the area.
"There are definitely lots of people who are afraid," Jacboson said. "I've talked to lots of folks who dropped off their children at Sunday school this morning, and I can't imagine, as a parent, what that would feel like."
Holzer commented on how mass shootings, like the one at the Treat of Life synagogue in Pittsburgh, have become more common during her lifetime.
"I'm thinking our world is a different place than the idyllic world I grew up in in Squirrel Hill," she said.
Police said there are no specific threats involving Chicago or this service, but they have increased police presence to provide additional comfort.
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